1. Field of the Invention
The present invention relates to a lens-fitted photographic film unit with a picture frame size changing device, and more particularly to a lens-fitted photographic film unit which is changeable between a panoramic size position and a standard or full size position.
2. Related Art
Compact cameras having a picture frame size changing device are known, wherein either full size photography or panoramic photography may be practiced in a strip of photographic film, and the field of view of the view of the viewfinder is also changed to correspond to either the full size or the panoramic size photographic field.
Also a lens-fitted photographic film units (hereinafter referred to as film units) are widely used, each of which contains a photographic film cassette and has a simple exposure mechanism and a fixed focus plastic lens, e.g., as disclosed in U.S. Pat. No. 4,884,087, so that anyone may enjoy photographing with ease at low cost. It is desirable to provide a picture frame size changing device in such a film unit.
In a picture frame size changing mechanism used in a conventional compact camera, a pair of light-shielding plates are disposed in a light-shielding box in front of an exposure aperture, so as to be movable into and out of an exposure light path between a panoramic size position and a full size position, respectively. The light-shielding plates are moved by sliding an operation member through an interconnecting mechanism. A toggle spring is provided for reliable positioning of the light-shielding plate in the respective switching positions. That is, the light-shielding plates move to either the panoramic or the full size position under the force of the toggle spring after the operation member is slid by a predetermined amount.
In order to switch over the direction of the biasing of the toggle spring in accordance with the sliding direction of the operation member, it is necessary to provide such a coupling member in the interconnecting mechanism that can push the toggle spring bidirectionally. It is also necessary to engage the coupling member, for example, a fork member with a pin for deforming or bending the toggle spring. However, this known inter connection mechanism could not maintain the light-shielding plates stable in the respective switching positions unless the mechanism is assembled after the light-shielding plates are positioned in one of the switching positions, and then the operation member is positioned in correspondence with the position of the light-shielding member.
The complicated and time consuming assembling process of the known frame size changing mechanism would increase the manufacturing cost. Moreover, the toggle spring needs a relatively large space for movement. Therefore, the conventional picture frame size changing device could not be preferably applied to the film unit which should be compact and inexpensive.
To solve this problem, an improvement has been suggested in U.S. Ser. No. 08/216,953, wherein a helical tension spring biases a pair of light-shielding plates toward the full size position, and the light-shielding plates, an interconnecting mechanism and a finder mask are coupled to one another through one-side contact.
However, because one-side contact coupling involves plays between the coupled members, it can be difficult to accurately position the light-shielding plates in the panoramic position. In that case, a picture frame that is intended to be panoramic size would be larger than the predetermined panoramic size, so that it might be mistaken as a full size picture frame by a film inspector. As a result, the picture frame to be printed in panoramic size would be unexpectedly printed in full size, producing a defective photo-print.